The "PCB-antenna" is equivalent to a 1 feet rod and though counter
intuitive, adding one won't help.
As with all active whip designs, at VLF / LF / MW and lower HF the
whip is NOT the antenna.
How the pa0rdt-Mini-Whip© works, can be found here:
Though some knowledgeable people don't agree, I have put the theory
to the test and build a battery powered mini-whip with the battery
included in the antenna housing. The rf was transported by a
optical fibre link. The antenna was mounted on a non conducting
fibre glass pole.
Nothing was received at all with this set up, until I put a coax
cable up the mast ending 5 cm below the antenna. There was no
connection between this cable and the circuit board, whatsoever.
The shield of the coax cable was connected to a ground stake at the
bottom of the mast and it provided the necessary ground reference
for the ohterwise isolated antenna.
I hope this helps.
Roelof Bakker, pa0rdt
N.B. Rather than building one for one's own use, which is no problem
at all, I am sorry to find that some people are making money from a
copywrighted design. (Readily build antennas are available from the
designer for those unable or unwilling to build one.)